Field of the Invention
The present invention relates to an ignition device for a safety system. More particularly, the present invention relates to an ignition device for a safety system for an air bag or a seat belt tightener of a motor vehicle.
AT 000 522 U1 discloses a driver for restraint systems in motor vehicles. The restraint consists of a housing with a cylinder in which a piston is movably disposed. The piston is forced out of the cylinder when a working chamber of the housing has been filled with pressure by the ignition of a propellant charge. The propellant charge is disposed in a portion of the housing which is separated from the working chamber by a so-called xe2x80x9cbursting bottom.xe2x80x9d Within the propellant charge, an ignition charge is present which, when the ignition charge has been fired, explodes the propellant charge.
The propellant charge, in which the ignition charge is concealed, is housed in a portion of the housing which is separated from this portion of the housing by a spacer sleeve. The ignition charge is connected by very thin leads to a control device. The portion of the housing in which the propellant charge is contained is closed by a cap.
Such prior art systems suffer from the disadvantage that they involve a very complicated construction. Moreover, the assembly of the entire ignition device is extremely costly, since many individual assembly steps must be performed by hand. Another disadvantage is that these process steps cannot be automated, or only automated ax very high, that is, prohibitive cost due to the indefinable position of the leads and the positioning of the ignition charge in the propellant charge. Furthermore, the testing of the ignition device suffers from the disadvantage that it can only be performed with the entire driving apparatus of the restraint system. Accordingly, this process step is also quite costly.
As disclosed in AT 000 522 U1, certain measures have been undertaken to prevent accidental ignition. However, another disadvantage of this driving device for restraint systems is that, despite the use of a cap, the propellant charge and the ignition charge (including the electrical leads) cannot be protected completely from environmental influences, especially moisture. As will be appreciated by one of ordinary skill in the art, if moisture penetrates into the propellant charge, its operation is no longer guaranteedxe2x80x94this is unacceptable in safety systems.
The present invention overcomes these disadvantages and offers new advantages as well.
According to the invention there is provided an ignition device for a safety system, such as an air bag or a safety seat belt tightener for a motor vehicle, including an igniter element which can be ignited through connecting means, such as connecting leads, wherein the ignition element is disposed and preassembled with the connecting means in an igniter housing.
According to one object of the invention, the ignition element with the connecting means, preferably connecting leads, are disposed and preassembled in an igniter case. Preferably, a preassembled unit is available which can be tested for its functionality before its installation. Moreover, it is possible to preassemble this ignition device independently of the safety system, such as the place where the safety system is installed. Accordingly, with regards to production, greater flexibility is provided since the manufacturer of the ignition device does not necessarily have to be the manufacturer of the safety system. Furthermore, one advantageous feature of the invention is that if the ignition device has been examined for proper operation, the ignition device can be installed in the propellent charge in the safety system without further examination.
According to the invention, the ignition element may be a triggering element for electrically actuated safety devices (on a pyrotechnic basis), such as the safety devices, especially air bags or seat belt tighteners, for motor vehicles. According to the invention, the ignition element may be dipped ignition heads as well as igniters in glass/metal form or the like.
In accordance with another aspect of the invention, the ignition element bears connecting lugs. In accordance with this aspect of the invention, the use of connecting lugs allows fastening of the ends of the connecting leads directly to the connecting lugs, preferably by soldering or welding. Alternative, in some cases a mechanical bond, such as crimping, may also be used.
In accordance with another aspect of the invention, at least one of the connecting lugs of the ignition element is connected by electrically conductive connecting means, such as stampings, to one of the terminals, especially one end of a connecting lead. Thus, the area between the point of installation of the ignition element in the igniter housing and the point of installation of the ends of the connecting means in the ignition housing can be bridged if this is necessary. As will be appreciated by one of ordinary skill in the art, through the use of stampings as electrically conductive connecting means, it is possible to automate the assembly process as well as the subsequent wiring since the stampings are rigid and thus provide precise positioning with respect to the other components (such as the igniter and connecting leads). Furthermore, it will be appreciated that it is possible to replace the electrically conductive connecting means, i.e, the stamping, with an electronic component. In accordance with one aspect of the invention, there is a coil or choke by means of which misfiring resulting from voltages or currents or line-bound radio frequency waves can be dissipated. Alternatively, instead of chokes or coils, components such as condensers, varistors or the like can also be used. Advantageously, SMD components can be used for compactness. According to another feature of the invention, the components can also be alternatively or additionally made parallel to the connecting means.
As will be appreciated by one of ordinary skill in the art, the use of stampings as electrically conductive connecting means thus has the advantage that the stampings can be delivered automatically and further processed at the same time the electrical contact is produced between the components involved.
According to another aspect of the invention, at least one connecting means, preferably one of the stampings, can be configured as an electrode. The stamping, or several stampings, configured as electrodes are brought out of the igniter housing to form (with the housing of the safety system) a spark gap through which voltages can be carried away which otherwise, if not removed, would result in triggering the igniter. Thus the use of a stamping as an electrode father improves compactness while simultaneously improving functionality.
In accordance with another aspect of the invention, at least the igniter, the connecting means (stampings) and the ends of the connecting means are arranged in an open housing, such as a half shell. In this open housing, which can also be automatically supplied, the positions of the igniter, the connecting means and the ends of the connecting means are provided, so that, after the components are placed in the open housing, the position of the components involved is preset and the contacting can be automated.
In accordance with another aspect of the invention, at least one of the connecting means, preferably the stampings, is arranged in an injection-molded housing. Preferably, the stampings are fixed in position and then the housing is made by an injection molding process, or other suitable process, whereby after the injection, a preassembled unit is the result. Preferably, this component can be delivered by automation to the next process step and processed further. For example, in the next process step, the insertion and connection of electronic components to the stampings may be performed. Also, as will be appreciated by one of ordinary skill in the art, the injection-molded housing is an open housing, so that the stampings are accessible for the insertion and connection of the components.
After the components have been inserted and connected, the open housing must be closed. According to one aspect of the invention, it is possible to close the housing with a potting composition which has the advantage that the process can also be automated, thereby resulting in a reliable electrical insulation of the components. Furthermore, the potting composition results in good protection of the electrical components against environmental influences, whereby malfunctions or outright failure due to moisture can be avoided. Moreover, short circuits should not develop since no electrically-conductive particles can penetrate into the housing and since components within the housing cannot come into contact due to vibration. The components inside of the housing are thus insulated electrically from one another. Additionally, by the use of an open housing and subsequent potting the rigidity of the entire system is definitely increased. Another advantage lies in the fact that the housing previously open and now sealed with the potting composition can continue to be processed by automation without problems.
Alternatively, it is possible for the open housing to be closed with a matching cover. If the cover has as its inner contours the external contours of the open housing, including the components involved, potting can be dispensed with. However, if this is not the case, i.e., there are still gaps between the inside contour of the cover and the outside contour of the open housing with its components, filling with a potting composition is possible. As will be appreciated by one of ordinary skill in the art, the same advantages may be realized using the matching cover as in the case of filling the open housing with a potting compound.
In both alternatives, there is an additional advantage, wherein by using a housing/potting compound or housing/cover (with potting compound in some cases), the ends of the connecting means are mechanically locked tight, resulting in better strain relief. Furthermore, greater water-tightness (lengthwise) may be obtained. Also, since the potting compound also envelops the connecting lugs and parts of the ignition element, the seal may be improved.
After the housing has been closed, it is surrounded by the igniter housing. The igniter housing may consist of at least two housing halves into which the closed housing with the ignition element and its connecting leads is inserted. Alternatively, it is possible to encase the closed housing with the ignition element (and its connecting leads) and the electrode by injection molding, wherein the igniter housing results from the injection molding. If the igniter housing is created by encasing it by injection molding, the rigid basic structure again produces an advantage since neither the ignition element nor the accompanying components (stampings etc.) can be damaged or impaired in their operation. Due to the basic structure of the sealed, formerly open housing, it is also possible to insert this basic structure automatically into the injection molding die. Surrounding the sealed housing with the igniter housing also helps ensure the sealing of the entire structure. Preferably, the external contours of the igniter housing are also configured such that automated further processing, such as testing and installation in the safety system, is possible.
An ignition device according to the invention, and various process steps for its manufacture, are described below with the aid of an enabling description of a presently preferred embodiment and with the aid of the figures. However, the invention should not be viewed as being limited to this embodiment.